CoronaVac: Effective and safe according to 2 large studies

The World Health Organization (WHO) gave emergency use approval to the vaccine on June 01, 2021 yet some people continue to regurgitate the narrative that “the vaccine is not effective.” 

Two new large studies of Sinovac’s CoronaVac inactivated vaccine showed good efficacy against symptomatic infection and severe disease. Perhaps now we can stop saying “we need more published data on CoronaVac.” 

However, if your issue is because the vaccine is from China or you are simply against everything recommended by authorities, no amount of data will be enough for you so don’t bother reading the rest of the article.

But if you are truly interested to know why WHO and 37 countries (so far) approved the vaccine, please continue reading. 

First study published in The Lancet: 83.5% efficacy against infection

Interim efficacy and safety results from a phase 3 trial in Turkey were published yesterday in The Lancet. A team led by researchers from Hacettepe University School of Medicine in Ankara randomly assigned either the inactivated CoronaVac vaccine or a placebo to 10,214 healthcare and community volunteers aged 18 to 59 years at 24 centers from Sep 14, 2020, to Jan 5, 2021. 

Participants received two doses of the vaccine or placebo 14 days apart. Over a median follow-up of 43 days in the Lancet study, 9 of 6,646 (0.14%) participants in the vaccine group and 32 of 3,568 (0.90%) in the placebo group had symptomatic COVID-19 at least 14 days after their second dose, for a vaccine efficacy of 83.5%.

No vaccinees were hospitalized, compared with six in the placebo group, for a vaccine efficacy against coronavirus-related hospitalization of 100%. 

While the analysis of immunologic tests done on a subset of participants is ongoing, early results show that 89.7% of vaccinees had antibodies against the coronavirus’s spike protein. Adverse events occurred in 18.9% of vaccinees and 16.9% in placebo recipients. No deaths or serious adverse effects were reported. 

Second study published in the NEJM: 65.9% protective against infection

A real-world study, published earlier this week in the New England Journal of Medicine, involved testing nearly 10.2 million Chilean residents 16 years and older who either had received at least one dose of CoronaVac or were unvaccinated against COVID-19 from Feb 2 to May 1, 2021. 

The team, led by researchers from the Chilean Ministry of Health, found an adjusted vaccine effectiveness against infection of 65.9% in participants who received two doses of CoronaVac at least 14 days before, with 87.5% protection against hospitalization, 90.3% effectiveness against intensive care unit (ICU) admission, and 86.3% effectiveness against coronavirus-related death.

Vaccine effectiveness in fully immunized participants 60 years or older was 66.6% against infection, 85.3% against hospitalization, 89.2% protective against ICU admission, and 86.5% effective against death. In participants who had received only the first dose at least 14 days before, vaccine effectiveness was only 15.5% against infection, 37.4% effective against hospitalization, 44.7% effective against ICU admission, and 45.7% protective against COVID-19 death. 

Among a subset of participants who had been tested for COVID-19 using polymerase chain reaction or antigen test during the analysis segment of the study, vaccination effectiveness was higher than when the whole cohort was included. Adjusted vaccine effectiveness among fully vaccinated participants in this group was 72.9% against infection, 89.2% against hospitalization, 91.6% against ICU admission, and 87.8% against death.

These two large studies suggest that CoronaVac had high effectiveness against severe disease, hospitalizations, and death, findings that underscore the potential of this vaccine to save lives and substantially reduce demands on the health care system. 

One of the advantages of CoronaVac is that it does not need to be frozen, making it easier to transport and distribute. This could be particularly important for global distribution, as some countries may struggle to store large amounts of vaccine at very low temperatures.


Dr. Melvin Sanicas (@Vaccinologist) is a physician-scientist specializing in vaccines, infectious diseases, and global health. 

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